An unmanned United States drone aircraft crashed in Pakistan's lawless northwestern tribal district on Sunday after suffering a technical fault, local security officials said.

The drone, the second to crash in Pakistan within the last month, went down in South Waziristan, part of the lawless tribal belt on the Afghan border that Washington calls a global headquarters of Al-Qaeda.

"The American drone crashed in Zangara village of South Waziristan, apparently because of some technical faults," a security official in Peshawar, the main town in Pakistan's northwest, told AFP.

Two intelligence officials in Wana, the main town of South Waziristan, confirmed the incident. It was an armed Predator drone, they said.

"A search operation is continuing to recover the debris," added a senior security official in Peshawar, saying that a group of militants fired on troops during the search operation but fled after retaliatory fire.

"We have no reports of loss of life on both sides," he added.

The United States uses unmanned surveillance aircraft in its war against the Taliban in Afghanistan to monitor militants in Pakistan, from where Al-Qaeda and Taliban-linked fighters launch attacks in Afghanistan.

It also uses Predator armed drones to launch missile attacks aimed at militants in Pakistan's unstable northwestern border areas.

US drone crashes are very rare in Pakistan, but a surveillance drone equipped with a camera crashed in southwestern Pakistan on August 25.

In September 2008, tribesmen in South Waziristan claimed to have shot down another surveillance drone in Jalal village, near the Afghan border.

The Pakistani army said at the time that it was investigating that incident but did not make the results of the probe public.

The US drone campaign is deeply unpopular among an anti-American Pakistani public and the government has publicly demanded an end to the attacks.

However, in private, Pakistani military and civilian leaders are thought to co-operate with the programme and Washington says it has been successful in eliminating a number of Al-Qaeda- and Taliban-linked militants in Pakistan.

Around two dozen drone strikes have been reported in Pakistan since elite US forces killed Al-Qaeda chief Osama bin Laden in a suburban home near Pakistan's main military academy in Abbottabad, close to the capital, on May 2.

The raid humiliated Pakistan and prompted allegations of incompetence and complicity in sheltering bin Laden.

Pakistan is seen as a key ally for the United States in its fight against Islamist militancy, but relations soured after the bin Laden raid, which both countries say was carried out without Islamabad being warned.